Contact method

The contact method can be used to obtain the complete set of stiffness constants for samples with much smaller dimensions. In this method [3,5], a piezoelectric ceramic transducer, bonded to one surface of the sample, generated a beam of pulsed 10 MHz elastic waves that was subsequently received by another transducer bonded to the opposite surface. The wave velocity was calculated from the transit time of the ultrasonic pulse measured on a gated time interval counter. Longitudinal and transverse waves were generated using two different types of transducers. 

To obtain all the independent stiffnesses of a material with orthorhombic symmetry, we have to measure nine independent velocities where 

The shear stiffnesses are derived from the transverse wave velocities  

It is noted that v y = Vy, so each shear stiffness can be derived from 

A sample with dimensions 3x1x1 mm is sufficient for obtaining the complete set of C- by the contact method. A larger dimension of 3 mm is used in the direction where the sample exhibits the highest extensional stiffness (such as the axis of an extruded PLC rod), so that the transit time is sufficiently long to ensure high accuracy. 

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Flaw detection by contact method of manual-manipulating 5MHz single creeping wave probe. 

FIG. 12-101 Alternative chambers and gas solids contacting methods in spray dryers. 

It is classification by contacting method that provides the two principal categories into which leaching equipment is divided (I) that in which the leaching is accomphshed oy percolation and (2) that in which particulate solids are dispersed into a hquid and subsequently separated from it. Each includes batch and continuous units. Materials which disintegrate during leaching are treated in equipment of the second class. 

Process and Operating Conditions The major parameters that must be fixed or identified are the solvent to be used, the temperature, the terminal stream compositions and quantities, leaching cycle (batch or continuous), contact method, and specific extractor choice. 

Leaching Cycle and Contact Method As is true generally, the choice between continuous and intermittent operation is largely a matter of the size and nature of the process of which the extraction is a part. The choice of a percolation or solids-dispersion technique depends principally on the amenability of the extraction to effective, sufficiently rapid percolation. 

Measurements using the Point Contact Method with Scanning Tunneling Microscopy. Journal of the American Chemical Society, 128, 7746-7747. 

Table VI. The knockdown power of the organofluorine insecticides has been determined principally against members of the Diptera order and by a limited number of workers. There is general agreement that DFDT acts more rapidly than DDT, at least against those species with which they have been compared. Prill 92) found that twice the amount of DFDT compared to DDT was required to give the same knockdown against houseflies when tested by a space spray technique with added pyrethrins. The forced contact method of Fay and Buckner 27) revealed that without added pyrethrins DFDT was a more powerful knockdown agent than DDT.

Gas-liquid mixtures are sometimes reacted in catalytic packed beds. Different contacting methods for gas-liquid reactions have been discussed in Section 7.3. 

Oguchi, U., and Kubo, J., Liquid-Solid Particles or Liquid-Gas-Solid Particle Contacting Method, U.S. Patent 3,754,993 (1973)... 

Like almost any other technique, thermoelectric power, does however also have some of its own limitations. For example, thermoelectric power is a contact method, which means that if hydrogen content needed to be measured on the exterior of a coated pipeline, the coating would need to removed, however in-line pig inspection would allow for in-situ inspection of the pipeline inner wall. In these limited cases, alternative complimentary techniques can be utilized. Low frequency impedance measurements can provide an alternative non-destructive, non-contact method of measuring hydrogen through an entire specimen thickness, dependent upon lift-off. 

Short-time phase contact methods These techniques do not stir the two phases, and the contact time between them is very short. 

The galvanic or contact method was the precursor to electrochemical treatment [283]. In an electrolytically conducting solution, the artifact is brought into contact with a piece of a less noble metal— usually zinc or aluminium. While the metal corrodes, the electrons supplied to the object allow the reduction of the tarnish layer. Although simple, this method presents some drawbacks, like the progressive contamination of the solution by the corrosion products of the active metal and also limitations with respect to the choice of applicable solution. 

Obviously to remove large amounts of asphaltic materials, substantial quantities of clay would be required in both the percolation and hot contacting methods, and the adsorption process then may become uneconomical in the treating of raw residua. With the exception of residual oils containing low concentrations of asphalts, oils to be treated with clay generally receive some pretreatment—for example, with sulfuric acid followed by neutralization of the acid oil, or selective solvent extraction. 

The baseline process, including the pressure sintering step, was demonstrated with both simulated high level waste and under hot cell conditions using a waste solution prepared from typical spent light water reactor fuel. A batch contacting method using sodium titanate was also evaluated, but the overall decontamination factor was much lower than obtained in the column process. 

Contact methods of measuring surface roughness (see Chapter 7) are not likely to be successful with uncured rubber because of its softness. It is unlikely that roughness needs to be known very precisely and a simple method has been given by Orlovskii et al139. The volume of a disc is calculated using the overall thickness measured on top of any irregularities and compared to the true volume measured by a liquid displacement method. 

The coefficient of linear expansion can be measured as an average over tens of °C to reasonable precision using a precision cathetometer. Most contact methods of measuring length are not suitable because of the low stiffness of rubber and, for the same reason, it is often necessary to support the test piece in a horizontal position. A convenient procedure is to lay a test piece on smooth rollers in a glass-sided bath, but it must be emphasised that only moderate precision can normally be obtained, unless an extremely sensitive optical measuring device is employed, and friction can never be eliminated. 

The same method is given in BS 903 Part A3782 which also contains a national annex giving a second method for assessing the degree of corrosion when the rubber is not in contact with the metal. Zinc is used as the standard metal as this is fairly readily corroded. A strip of zinc and the rubber test piece are both suspended over distilled water in a stoppered container maintained at 50°C. After a period of three weeks, the corrosion products are removed from the zinc by immersion in chromium trioxide solution and the loss in weight used as the measure of degree of corrosion. This is a very sensitive method but even more care has to be taken than in the contact method to avoid contamination and to obtain reproducible results. 

In this chapter we take a careful look at the phenomenon of electrical conductivity of materials, particularly electrolytic solutions. In the first section, the nature of electrical conductivity and its relation to the electrolyte composition and temperature is developed. The first section and the second (which deals with the direct-current contact methods for measuring conductance) introduce the basic considerations and techniques of conductance measurement. This introduction to conductance measurements is useful to the scientist, not only for electrolytic conductance, but also for understanding the applications of common resistive indicator devices such as thermistors for temperature, photoconductors for light, and strain gauges for mechanical distortion. The third section of this chapter describes the special techniques that are used to minimize the effects of electrode phenomena on the measurement of electrolytic conductance. In that section you will encounter the most recent solutions to the problems of conductometric measurements, the solutions that have sparked the resurgent interest in analytical conductometry. 

The best technique for lower resistances is the four-contact method shown in Figure 8.6. The leads and contacts that measure the voltage across the resistor, caused by the current through the resistor, are not the same leads and contacts that supply the current. Since the current does not appear in the voltmeter leads or contacts, no error due to an iR voltage in the voltmeter contacts will occur. 

There is a wide choice of contacting methods and equipment for gas-solid reactions. As with other solids-handling problems, the solution finally adopted may depend very much on the physical condition of the reactants and products, i.e. particle size, any tendency of the particles to fuse together, ease of gas-solid separation, etc. One type of equipment, the rotary kiln, has already been mentioned (Chapter 2, Fig. 2.4) and some further types of equipment suitable for continuous operation are shown in Fig. 3.37. The concepts of macromixing in the solid phase and dispersion in the gas phase as discussed in the previous section will be involved in the quantitative treatment of such equipment. 

Particle size distributions of the reactant as well as of the product powders, were measured by a HORIBA (model CAPA-700) particle size analyzer. This instrument uses a non-contact method based on liquid-phase sedimentation, and has a measuring range between 0.01 and 300 pm. 

Adsorption can be carried out by stagewise or continuous-contacting methods. The stagewise operation of adsorption is called contact filtration because the liquid and the solid are contacted in a mixer and then the solid is separated from the solution by filtration. 

Because the spatial area with higher temperature on the catalyst surface of one of the samples of the library is very small the detection of catalytic activities through temperature measurement cannot be carried out by direct temperature measurements but only by non-contact methods such as pyrometry or IRT. The IR video camera used here measures the emission at every point of the library in parallel. The detector consists of a 256x256 pixel array of Pt-silicide-IR-sensors. Each pixel delivers a voltage-signal that depends on the infrared radiation and the sensitivity of that pixel (fixed pattern noise). 

To avoid electrolysis and electrode fouling when the solution was in contact with the measurement electrodes, contactless conductivity detection was proposed. This non-contact method relied on the capacitive coupling of the electrolyte in the channel, and the method has been used to detect inorganic ions that alter the conductivity and capacitance in the electrolyte [277,638]. 

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